1. Field of the Invention
This invention relates to an extra-fine copper alloy wire, an extra-fine copper alloy twisted wire, an extra-fine insulated wire, a coaxial cable, and a multicore cable. In particular, this invention relates to the extra-fine copper alloy wire, an extra-fine copper alloy twisted wire, an extra-fine insulated wire, a coaxial cable, and a multicore cable that have both of a high mechanical strength and a high electrical conductivity, and also have a high heat resistance to suppress a reduction in its mechanical strength even in a heat load work such as an extrusion work, an foam extrusion work and a soldering work. Also, this invention relates to methods of making the extra-fine copper alloy wire, the extra-fine copper alloy twisted wire, the extra-fine insulated wire, the coaxial cable, and the multicore cable.
2. Description of the Related Art
Copper alloys with a high mechanical strength and a high electrical conductivity are generally used as conductor materials of flexing cables for an electric device such as a robot cable, and for a medical device such as a probe cable.
At present, mass-produced copper alloy wires are formed of a Cu—Sn alloy wire and a Cu—Sn—In alloy wire which are applicable to continuous casting and rolling, and excellent in economic efficiency and which are in wide use as conductor materials of the flexing cables for the electric device and the medical device. The other copper alloy wires are also applied to various fields according to the product cost and various characteristics of copper alloy wire.
In recent years, conductors with φ0.03 mm or less have been required according as the electric device is reduced in size and weight and as the medical device is downsized. In particular, according as a head portion of an ultrasonic endoscope is sophisticated, a cable for the ultrasonic endoscope tends to increase in number of cores (e.g., 200 to 260 cores). On the other hand, the head portion is required to decrease in diameter to mitigate the pain of a patient. In case of a curl cable etc. used for performing an intravascular operation approaching from a vascular space to an affected part, the downsizing of the diameter is also required.
Further, recently, the development of conductor materials to satisfy both a high mechanical strength and a high electrical conductivity as well as the reduced diameter has been desired to improve its flexibility and to increase its transmission capacity.
The Cu—Sn alloy wire and the Cu—Sn—In alloy wire as described above are formed of a copper alloy produced by adding tin (Sn) to a tough pitch copper as a base metal. However, since the amount of Sn added need to be increased to enhance the mechanical strength of the Cu—Sn alloy wire, the electrical conductivity must be lowered. Thus, it is difficult to satisfy both the mechanical strength and the electrical conductivity.
In recent years, a Cu—Ag alloy has drawn attention as a copper alloy to satisfy both the mechanical strength and the electrical conductivity. The Cu—Ag alloy excellent in mechanical strength and electrical conductivity is produced, for example, by (1) casting a Cu—Ag alloy with a Ag content of 1.0 to 15 weight % and then cold-working the cast Cu—Ag alloy to an area reduction of 70% or more, (2) conducting a heat treatment at 400 to 500° C. for 1 to 230 hours, and (3) cold-working it to an area reduction of 95% or more (See JP-A-2001-40439).
Further, a method of making an extra-fine copper alloy twisted wire is known which is conduced by adding 0.1 to 1.0 weight % of silver to a pure copper to have a Cu—Ag alloy, forming a single wire with a diameter of 0.01 to 0.08 mm and a tensile strength of 600 MPa or more from the alloy, twisting a predetermined number of the wires together, and conducting a heat treatment to the twisted wire to remove distortion thereof (See JP-A-2001-234309).
In case of using the extra-fine copper alloy wire formed of Cu—Ag alloy as a flexing cable, an insulating material is generally extruded to cover it. In this extruding, the insulating material is heated to cause a heat load to the extra-fine copper alloy wire. Therefore, required as characteristics for the extra-fine copper alloy wire is not only the mechanical strength and the electrical conductivity but also a heat stability that the strength is not lowered by a heat history in the extruding.
For example, the insulating material with a melting point of approx. 300° C. is generally extruded to cover it. Thus, in the extruding, the mechanical property thereof, especially, the tensile strength is lowered by heat (e.g., 300 to 380° C.) of the insulating material and an extruder head part during the covering process. Further, in the terminal processing, the tensile strength of a terminal portion of the extra-fine copper alloy wire is significantly lowered by a heat of soldering iron at approx. 300 to 350° C. during the soldering. Therefore, after the extruding or the soldering, it may be difficult to satisfy both the electrical property and the mechanical property. The mechanical reliability of the cable and the cable terminal work portion may be significantly damaged by the lowering of, especially, the tensile strength.
In case of a coaxial cable with a low capacitance, a foamed insulating material is generally extruded and covered it at its melting point of approx. 300° C. In the extruding process, the mechanical property of the extra-fine copper alloy wire, in particular, the tensile strength is lowered by heat (e.g., 300 to 380° C.) of the insulating material and an extruder head part during the covering process. In the terminal processing, the tensile strength of a terminal portion of the extra-fine copper alloy wire is significantly lowered by a heat of a soldering iron at approx. 300 to 350° C. during the soldering. Therefore, after the extruding and the soldering, it may be difficult to satisfy both the electrical property and the mechanical property. The mechanical reliability of the cable and the cable terminal work portion may be significantly damaged by the lowering of, especially, the tensile strength.
Further, an extra-fine wire with a diameter of about 0.025 mm or less is used for a probe cable of a ultrasonic diagnostic equipment and for a ultrasonic endoscope cable, where an electrical resistance corresponding to a conductor size becomes problematic. For example, such an extra-fine copper alloy twisted wire needs to satisfy truly both a reduced diameter and an enhanced electric property need while complying with the AWG (American Wire Gauge) standards. A relationship between the AWG standards and the twisted wire structure (i.e., number of twisted wires/wire diameter) needs to be 42 AWG (7/0.025), 43 AWG (7/0.023), 44 AWG (7/0.020), 45 AWG (7/0.018), 46 AWG (7/0.016), 48 AWG (7/0.013), 50 AWG (7/0.010).
However, although the Cu—Ag alloy in JP-A-2001-234309 satisfies both the tensile strength and the electrical conductivity, the heat treatment needs to be conducted at a specific temperature for the long time (1 to 30 hours) so that the production efficiency is reduced to increase the manufacturing cost. JP-A-2001-234309 does not teach the lowering of the strength caused by the heat history when a heat load is applied thereto in the extruding process, and does not show any measures for it. Further, it does not teach the electrical resistance corresponding to the extra-fine conductor size.
Although JP-A-2001-234309 discloses the extra-fine copper alloy twisted wire that comprises silver as an additional element to the copper alloy, the silver content is as low as 0.1 to 1.0 weight % so that improvement of the tensile strength can not be expected. In this extra-fine copper alloy twisted wire, an elongation of 5% or more is secured to improve its flexibility in plastic distortion region, but the tensile strength must be lowered under such a property emphasizing the elongation. Therefore, the strength and the flexibility become inadequate for use as an electronics device cable or a medical device cable using extra-fine wires with a diameter of 0.025 mm or less, such as a probe cable of a ultrasonic diagnostic instrument and as ultrasonic endoscope cable.